Photomask blank and method for manufacturing photomask blank

ABSTRACT

The present invention relates to a photomask blank obtained by forming a resist film after performing a silylation process on a silicon-containing inorganic film and provides a method for manufacturing a photomask blank having at least a silicon-containing inorganic film over a transparent substrate and a resist film on the silicon-containing inorganic film, comprising: forming the silicon-containing inorganic film such that a surface that will contact the resist film has an oxygen concentration not less than 55 atomic percent and not more than 75 atomic percent; performing a silylation process after forming the silicon-containing inorganic film; and then forming the resist film by application. The method can inhibit generation of defects due to resist residues or the like after development.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photomask blank for a photomask foruse in fabrication of a semiconductor integrated circuit and the likeand a method for manufacturing a photomask blank.

2. Description of the Related Art

In recent semiconductor processes, particularly the increasing scale ofintegration of large-scale integrated circuits increasingly requires theshrinking of circuit patterns. There is a growing demand for shrinkingtechniques of wiring patterns formed in circuits or contact holepatterns for wiring between layers formed in cells. In production ofphotomasks, in which circuit patterns are formed, for use in opticalphotolithography for forming these wiring patterns or contact holepatterns, there is accordingly a need for a technique to precisely formfiner circuit patterns due to the above shrinking of the patterns.

Forming a resist pattern with high precision on a photomask blank isfirst needed to form a photomask pattern with higher precision on aphotomask substrate. When an actual semiconductor substrate isprocessed, since optical photolithography employs reduced-sizeprojection, the photomask pattern needs a size that is about four timesgreater than an actually needed pattern size. This however does not meanthat the required precision is accordingly lowered, but a higherprecision than that of the pattern after exposure is rather needed for aphotomask serving as an original.

In addition, photolithography currently employed draws a circuit patternwith a significantly lower size compared with a wavelength of light tobe used. Accordingly, if a photomask pattern having a size four timesgreater than that of a circuit form is used, then the photomask patternform is not accurately transferred to a resist film due to influence oflight interference occurring when the optical photolithography isperformed, etc. For the purpose of reducing the influence, the photomaskpattern sometimes needs to be formed into a more complex form (a form towhich optical proximity correction (the so-called OPC) is applied) thanan actual circuit pattern. There is accordingly a need for ahigher-precision processing method in the photolithography technique toobtain photomask patterns. The performance of lithography may berepresented by a resolution limit. The lithography technique inphotomask forming processes requires a resolution limit substantiallyidentical to or more than the resolution limit needed in opticalphotolithography employed in semiconductor processes using photomasks.

The procedure for forming a photomask pattern typically involves forminga photoresist film on a photomask blank having a light-shielding film ona transparent substrate, drawing a pattern by an electron beam,obtaining a resist pattern through development, and then etching thelight-shielding film to form a light-shielding pattern while using theobtained resist pattern as an etching mask. If it attempts to achievethe shrinking of the light-shielding pattern while the same thickness ofthe resist film as that before the shrinking is maintained, then a ratioof a film thickness to the pattern, i.e., the an aspect ratio, becomeslarger and pattern transfer thereby fails due to deterioration of thepattern form of the resist, or the resist pattern is broken or separatedin some cases. The shrinking accordingly necessitates thinning a resistfilm thickness.

Use of hard masks has been tried before to reduce a burden on resistsduring dry etching. For example, Patent Document 1 reports that an SiO₂film formed on MoSi₂ is used as an etching mask when MoSi₂ is dry etchedwith a gas containing chlorine, and the SiO₂ film can also function asan antireflection coating. In addition, there is disclosed that chromiumis used for a light-shielding film on a phase shift film and an SiO₂film on the light-shielding film is used as a hard mask in, for example,Patent Document 2.

PRIOR ART REFERENCES Patent Literature

-   Patent Document 1: Japanese Unexamined Patent publication (Kokai)    No. S63-85553-   Patent Document 2: Japanese Unexamined Patent publication (Kokai)    No. H7-49558

SUMMARY OF THE INVENTION Technical Problem

The above-described shrinking of patterns makes adhesion of resistsimportant. If a fine pattern with a size of, e.g., 50 nm or less isformed in a film containing Si on its surface above a photomask, thenthe resist pattern is separated due to poor adhesion to the filmcontaining Si during development. It has been known that performing asilylation process using, e.g., hexamethyldisilazane is effective inavoiding the separation.

There however arises a problem in that the silylation process giveshydrophobicity to a surface and thereby makes cleaning of the surfacedifficult; thereby many resist residues remain in a cleaning processafter development, resulting in defects. It is only necessary forimprovement in cleaning ability to improve wettability by usingisopropyl alcohol or the like. These solvents however adversely affectresist patterns.

The present invention was accomplished in view of the above-describedproblems and relates to a photomask blank in which a resist film isformed after a silicon-containing inorganic film is subjected to asilylation process. It is an object of the present invention to providea photomask blank and a method for manufacturing a photomask blank thatcan inhibit generation of defects due to resist residues or the likeafter development.

Solution to Problem

To achieve this object, the present invention provides a method formanufacturing a photomask blank having at least a silicon-containinginorganic film over a transparent substrate and a resist film on thesilicon-containing inorganic film, comprising: forming thesilicon-containing inorganic film such that a surface that will contactthe resist film has an oxygen concentration not less than 55 atomicpercent and not more than 75 atomic percent; performing a silylationprocess after forming the silicon-containing inorganic film; and thenforming the resist film by application.

The present invention also provides a method for manufacturing aphotomask blank having at least a silicon-containing inorganic film overa transparent substrate and a resist film on the silicon-containinginorganic film, comprising: forming the silicon-containing inorganicfilm such that when a surface that will contact the resist film issubjected to X-ray photoelectron spectroscopy, a detected intensity withrespect to an Si—O bond energy is larger than a detected intensity withrespect to an Si—Si bond energy; performing a silylation process afterforming the silicon-containing inorganic film; and then forming theresist film by application.

According to the above methods, the adhesion between thesilicon-containing inorganic film and the resist film can be improved bythe silylation process, and even when a fine pattern is formed in theresist film, falling and separation of the resist pattern can beinhibited.

In addition, since the resist film is formed after thesilicon-containing inorganic film having a surface fulfilling the aboveconditions is formed, generation of resist residues after development,which are conventionally generated in the case of performing asilylation process, can be inhibited, and the number of defects canthereby be reduced.

Moreover, the silicon-containing inorganic film (when a surface thatwill contact the resist film is subjected to X-ray photoelectronspectroscopy, a detected intensity with respect to an Si—O bond energyis larger than a detected intensity with respect to an Si—Si bondenergy) may be formed such that the surface that will contact the resistfilm has an oxygen concentration not less than 55 atomic percent and notmore than 75 atomic percent.

According to the above method, the number of defects can be moreassuredly reduced.

In the method, hexamethyldisilazane may be used for the silylationprocess.

Use of Hexamethyldisilazane (also referred to as HMDS, hereinafter) ispreferred because it is commonly used in processes of semiconductorfabrication, such as photomask blanks.

Moreover, the silicon-containing inorganic film may further contain atleast one of oxygen and nitrogen.

Forming the silicon-containing inorganic film further containing atleast one of oxygen and nitrogen as above is more preferable.

Moreover, the silicon-containing inorganic film may be an SiO film or anSiON film.

Thus, an SiO film or an SiON film is particularly preferable as thesilicon-containing inorganic film.

In the method, the silicon-containing inorganic film may be formed insuch a manner that an inorganic film containing silicon is depositedover the transparent substrate and then subjected to a heat treatment,an ozonation treatment, or a plasma treatment.

The silicon-containing inorganic film may be alternatively formed overthe transparent substrate through deposition by sputtering.

In this manner, a silicon-containing inorganic film having a surfacefulfilling the above conditions can readily be formed.

Furthermore, the present invention provides a photomask blank comprisingat least a silicon-containing inorganic film over a transparentsubstrate, the silicon-containing inorganic film being subjected to asilylation process, and a resist film on the silicon-containinginorganic film, wherein the silicon-containing inorganic film isconfigured such that a surface that contacts the resist film has anoxygen concentration not less than 55 atomic percent and not more than75 atomic percent.

The present invention also provides a photomask blank comprising atleast a silicon-containing inorganic film over a transparent substrate,the silicon-containing inorganic film being subjected to a silylationprocess, and a resist film on the silicon-containing inorganic film,wherein the silicon-containing inorganic film is configured such thatwhen a surface that contacts the resist film is subjected to X-rayphotoelectron spectroscopy, a detected intensity with respect to an Si—Obond energy is larger than a detected intensity with respect to an Si—Sibond energy.

Such photomask blanks can inhibit falling and separation of the resistpattern even when a fine pattern is formed in the resist film, and alsoinhibit generation of resist residues, thereby reducing the number ofdefects.

Moreover, the silicon-containing inorganic film (when a surface thatcontacts the resist film is subjected to X-ray photoelectronspectroscopy, a detected intensity with respect to an Si—O bond energyis larger than a detected intensity with respect to an Si—Si bondenergy) may be configured such that the surface that contacts the resistfilm has an oxygen concentration not less than 55 atomic percent and notmore than 75 atomic percent.

Such photomask blank can more assuredly reduce the number of defects.

Moreover, Hexamethyldisilazane may be used for the silylation process.

HMDS is preferred because it is commonly used in processes ofsemiconductor fabrication, such as photomask blanks.

Moreover, the silicon-containing inorganic film may further contain atleast one of oxygen and nitrogen.

Forming the silicon-containing inorganic film further containing atleast one of oxygen and nitrogen as above is more preferable.

Moreover, the silicon-containing inorganic film may be an SiO film or anSiON film.

Thus, an SiO film or an SiON film is particularly preferable as thesilicon-containing inorganic film.

Advantageous Effects of Invention

As described above, the inventive photomask blank and method formanufacturing a photomask blank can inhibit falling and separation of aresist pattern and generation of resist residues after exposure anddevelopment, so the number of defects can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example of the inventive photomaskblank;

FIG. 2 is a flowchart of an example of the inventive method formanufacturing a photomask blank;

FIG. 3 is a graph showing a detected intensity with respect to an Si—Obond energy and a detected intensity with respect to an Si—Si bondenergy by an ESCA method (an XPS method) in Examples 1, 2 andComparative Example.

FIG. 4 is an observation view showing defects distribution afterdevelopment in Example 1; and

FIG. 5 is an observation view showing defects distribution afterdevelopment in Comparative Example.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will now be specificallydescribed with reference to figures, but the present invention is notlimited to this embodiment.

The present inventors diligently studied photomask blanks. As describedabove, when a resist film is formed after a silicon-containing inorganicfilm is subjected to a silylation process, conventionally, many resistresidues are generated after the resist film is exposed and developed.The present inventors, in contrast, found that adjusting the oxygenconcentration or the like of a surface of a silicon-containing inorganicfilm enables defects such as resist residues to be dramatically reducedeven when a resist pattern is formed through the following silylationprocess, application of a resist, and development, thereby brought thepresent invention to completion.

FIG. 1 shows an example of the inventive photomask blank. As shown inFIG. 1, in a photomask blank 1 of the present invention, for example, aphase shift film 3, a light-shielding film 4, a silicon-containinginorganic film 5, and a resist film 6 is formed in this order on atransparent substrate 2.

The transparent substrate 2 for use in the photomask blank 1 may becomposed of, but not limited to, a material that is transparent to anexposure light wavelength and has small amounts of thermal deformationat temperatures in manufacturing processes; a quartz substrate is givenas an example of this material.

Next, the structure of films over the transparent substrate 2 will bedescribed.

The silicon-containing inorganic film 5 needs to fulfill predeterminedconditions, such as an oxygen concentration, of its surface thatcontacts the resist film 6, as described below. The silicon-containinginorganic film 5 itself may be an inorganic film containing, forexample, silicon; or silicon and at least one selected from a groupincluding oxygen, nitrogen and carbon; or silicon and transition metal;or silicon, transition metal and at least one selected from a groupincluding oxygen, nitrogen and carbon. Examples of such an inorganicfilm include an inorganic film composed of silicon; or oxygen andsilicon; or nitrogen and silicon; or oxygen, nitrogen and silicon; orcarbon and silicon; or carbon, oxygen and silicon; or carbon, nitrogenand silicon; or carbon, oxygen, nitrogen and silicon. Examples of aninorganic film containing transition metal include an inorganic filmcomposed of transition metal and silicon; or transition metal, siliconand oxygen; or transition metal, nitrogen and silicon; or transitionmetal, oxygen, nitrogen and silicon; or transition metal, carbon andsilicon; or transition metal, carbon, oxygen and silicon; or transitionmetal, carbon, nitrogen and silicon; or transition metal, carbon,oxygen, nitrogen and silicon. A silicon-containing inorganic filmcomposed of silicon, oxygen and nitrogen (an SiON film); or silicon andoxygen (an SiO film) is particularly desirable.

Examples of the transition metal include molybdenum, tungsten, tantalum,titanium, zirconia, and hafnium. The silicon-containing inorganic film 5is not limited to a kind of a contained transition metal and may containtwo kinds or more of transition metals.

Hydrogen may also be contained.

The silicon-containing inorganic film 5 is subjected to the silylationprocess. The silicon-containing inorganic film 5, which is subjected tothe silylation process, thereby has high adhesion to the resist film 6formed thereon. The occurrence of falling and separation of a resistpattern can thereby be inhibited even when a fine pattern is formed inthe resist film 6.

The silylation process performed on the silicon-containing inorganicfilm 5 may be for example, but not limited to, a process using HMDS,which is commonly used in semiconductor fabrication processes.

In addition, the silicon-containing inorganic film 5 is configured suchthat its surface that contacts the resist film 6, i.e., a contactsurface 7, has an oxygen concentration not less than 55 atomic percentand not more than 75 atomic percent (the first embodiment).

In conventional photomask blanks using a silylation process, many resistresidues are generated and cause defects after development. In contrast,the inventive photomask blank 1 having the contact surface 7 satisfyingthe above condition can inhibit the generation of resist residues, whichare generated in conventional photomask blanks, and reduce the number ofdefects.

The reason for the reduction in defects by the oxygen concentration ofthe contact surface 7 of the silicon-containing inorganic film 5 isunclear; for example, it can be understood that the reason is that theamount of OH in the contact surface 7 or a bonding status of atoms inthe contact surface 7 changes.

Alternatively, the silicon-containing inorganic film 5 is configuredsuch that when the contact surface 7 is subjected to X-ray photoelectronspectroscopy (the XPS method), a detected intensity with respect to anSi—O bond energy is larger than a detected intensity with respect to anSi—Si bond energy (the second embodiment).

Such a silicon-containing inorganic film, which has the aboverelationship between detected intensities with respect to the Si—O bondenergy and the Si—Si bond energy, can inhibit resist residues and reduceits defects after development as in the first embodiment.

Alternatively, the silicon-containing inorganic film 5 may meet both ofthe above conditions. Such photomask blank can more assuredly reduce thenumber of defects.

It is only necessary for the structure of films to locate thesilicon-containing inorganic film 5 directly under the resist film 6;the silicon-containing inorganic film 5 may function as, for example, anoptical film such as a light-shielding film or a phase shift film, or ahard mask film for use in forming a pattern on the optical film, andalso have an etching stopper.

The present invention is particularly effective when a fine pattern,e.g., with a size of 50 nm or less, is formed. This effect is increasedwhen the silicon-containing inorganic film 5 is used as a hard maskfilm.

When the silicon-containing inorganic film 5 is used as a hard maskfilm, the film thickness of the hard mask film is preferably 1 to 30 nm,further preferably 1 to 20 nm, more preferably 1 to 10 nm.

In the configuration in this embodiment, a light-shielding film 4 and aphase shift film 3 below the light-shielding film 4 are formed betweenthe silicon-containing inorganic film 5 serving as the hard mask filmand the transparent substrate 2. The silicon-containing inorganic film 5serving as the hard mask film and the light-shielding film 4 preferablyhave etching selectiveness.

If the hard mask (etching mask) film (i.e., the silicon-containinginorganic film 5) is composed of a material that can be dry etched witha fluorine-based etching gas containing fluorine such as CF₄ or SF₆,then the etching process becomes easier; if the light-shielding film 4and the other inorganic films formed below the above hard mask film arecomposed of a material that has resistance against the fluorine-baseddry etching and can be etched by chlorine-based dry etching with anetching gas containing chlorine or chlorine and oxygen, then the etchingprocess becomes easier. The light-shielding film 4 and the otherinorganic films formed below the above hard mask film are desirablyinorganic films containing chromium: for example, a film containingchromium, or chromium and at least one selected from a group includingoxygen, nitrogen and carbon. An antireflection layer may be formed onthe hard mask film side of the light-shielding film 4, and a filmcontaining a large amount of oxygen or nitrogen may be formed on itstransparent substrate side to improve the adhesion and to be used as anantireflection film.

When the phase shift film 3 is formed between the light-shielding film 4and the transparent substrate 2, the phase shift film 3 preferably hasdifferent etching properties from the light-shielding film 4. If thelight-shielding film 4 has resistance against the fluorine-based dryetching and can be dry etched with an etching gas containing chlorineand oxygen as above, the phase shift film 3 need only be composed of amaterial that has resistance against dry etching with an etching gascontaining chlorine and oxygen and can be etched by the fluorine-basedetching; for example, a material containing silicon and at least oneselected from a group including oxygen, nitrogen, and carbon may beused, or a transition metal may further be contained. Examples of thetransition metal include molybdenum, tungsten, tantalum, titanium,zirconia, and hafnium. Hydrogen may further be contained.

If a light-shielding film is located below the resist film 6, then thematerial containing silicon may be the above-described material and theentire light-shielding film may serve as the silicon-containinginorganic film 5. If an antireflection layer is formed on the surface ofa light-shielding film, then the antireflection layer (only) may serveas the silicon-containing inorganic film 5 and the light-shielding filmmay be formed of another material such as a chromium-containing film.

The material of the resist film 6 may be an electron beam resist for usein drawing with an electron beam or a photoresist for use in drawingwith light. A chemically amplified resist is particularly effective. Thechemically amplified resist may be either a positive type or a negativetype, and composed of a resin based on hydroxystyrene or mainly an acidgenerating agent; a cross-linking agent may be added; at least one ofquencher, surfactant and the like may be added; a (meth)acrylic acidresin may be used.

Next, the inventive method for manufacturing a photomask blank 1 asshown in FIG. 1 will be described. FIG. 2 is a flowchart of an exampleof the inventive manufacturing method.

A transparent substrate 2 is first prepared (FIG. 2 at (A)). The abovetransparent substrate, for example a quartz substrate, may be preparedas the transparent substrate 2.

Next, a phase shift film 3 (FIG. 2 at (B)) composed of the abovematerial, and a light-shielding film 4 (FIG. 2 at (C)) are formed inthis order. The method of forming these films may be for example, butnot limited to, sputtering.

Next, a silicon-containing inorganic film 5 composed of theabove-described material is formed (FIG. 2 at (D1) or FIG. 2 at (D2a)-(D2 b)). The silicon-containing inorganic film 5 is formed such thata surface (i.e., a surface that will contact a resist film 6 formed in alater step) has an oxygen concentration not less than 55 atomic percentand not more than 75 atomic percent, or when being subjected to X-rayphotoelectron spectroscopy, the surface exhibits a detected intensitywith respect to an Si—O bond energy larger than a detected intensitywith respect to an Si—Si bond energy. Alternatively, thesilicon-containing inorganic film 5 may be formed such that thesilicon-containing inorganic film meets both of the above conditions.

After the oxygen concentration of the surface is adjusted as above, asilylation process, which is described later, is performed, and a resistfilm is then formed by application. This procedure enables generation ofresist residues to be inhibited when a pattern is drawn in the resistfilm 6 and developed as compared with conventional products, therebysignificantly reducing the number of defects.

For the purpose of forming the silicon-containing inorganic film 5 inwhich its surface fulfills conditions such as oxygen concentration, forexample, conditions under which the silicon-containing inorganic film 5is deposited by sputtering may be adjusted (FIG. 2 at (D1)).

Alternatively, an inorganic film containing silicon (a preliminaryinorganic film 8) is first deposited (FIG. 2 at (D2 a)) and thensubjected to a heat treatment, an ozonation treatment, a plasmatreatment, or the like to adjust the oxygen concentration or the like ofthe surface, whereby the silicon-containing inorganic film 5 can beformed (FIG. 2 at (D2 b)).

These methods are preferable because the silicon-containing inorganicfilm 5 having such a surface can readily be formed.

The method of forming the silicon-containing inorganic film 5 and thepreliminary inorganic film 8 may be chemical vapor deposition (CVD) witha gas containing silicon, such as, for example, monosilane,dichlorosilane, or trichlorosilane; forming the film by sputtering usingat least one target containing silicon is preferable because thissputtering is easier and has good controllability.

The method of forming the film by sputtering may be, but notparticularly limited to, DC sputtering, RF sputtering, or the like. Information of the silicon-containing inorganic film 5, when the inorganicfilm to be formed contains, for example, silicon and oxygen, reactivesputtering may be performed with silicon as a target and a gas of argonand oxygen as a sputtering gas. When the inorganic film to be formedcontains nitrogen instead of oxygen, a nitrogen gas may be used insteadof the oxygen gas. When the inorganic film to be formed contains bothnitrogen and oxygen, a nitrogen gas and an oxygen gas may be used at thesame time, or a nitrogen oxide gas such as nitrogen monoxide or nitrogendioxide may be used. When the inorganic film to be formed furthercontains carbon, a gas containing carbon such as a methane gas, a carbonmonoxide gas, or a carbon dioxide gas may be used. When the inorganicfilm to be formed further contains transition metal, a target includingtransition metal and silicon may be used, or cosputtering with both asilicon target and a transition metal target may be performed.

In addition, the silicon-containing inorganic film formed by depositionas above preferably has the Si—Si bonds because the Si—O bonds of thesurface of this film can be controlled by a heat treatment under anoxygen-containing gas.

If the oxygen concentration of the surface is adjusted by adjustingdepositing conditions in sputtering, for example, then the oxygenconcentration may be adjusted by adjusting a ratio of an oxidizing gassuch as oxygen or carbon dioxide to an inert gas such as argon in anatmosphere gas under which deposition is performed.

If the oxygen concentration of the surface is adjusted by a heattreatment, on the other hand, the oxygen concentration in a heattreatment atmosphere may be for example, but not limited to, 1 to 100%.The heat treatment may be, but not limited to, infrared heating,resistance heating, or the like.

The temperature of the heat treatment in the atmosphere including oxygenis preferably 200° C. or more, further preferably 400° C. or more.

Conditions under which an ozonation treatment, a plasma treatment, orthe like is performed are also not limited. The conditions of thesetreatment may be adjusted appropriately such that the oxygenconcentration of the surface, etc., fulfills the above condition.

Cleaning may be then performed (FIG. 2 at (E)). This cleaning to removeparticles present on the surface of a photomask blank may be performedby using ultrapure water, or functional water, such as ultrapure watercontaining ozone, hydrogen, or the like, and applying ultrasonic waves.Alternatively, cleaning with ultrapure water including surfactant may befollowed by rinsing with ultrapure water, and the above functional watercleaning, ultraviolet light irradiation, or the combination thereof maybe performed.

The silylation process is then performed to reduce surface energy of aphotomask blank surface such that the photomask blank surface isalkylsilylated (FIG. 2 at (F)). Such a silylation process allows a fineresist pattern to be prevented from being separated and fallen.

The above HMDS is given as an example of a silylation agent, but doesnot limit the silylation agent.

Known silylation processes include a method of directly applying thesilylation agent to the silicon-containing inorganic film of thesubstrate and a method of exposing the substrate to the silylationagent.

Known exposing methods include a method of evaporating the silylationagent in a container holding the substrate and a method of vaporizingthe silylation agent by bubbling of a nitrogen gas. The temperature atwhich the silylation agent is reacted may be, for example, in the rangefrom 40° C. to 200° C. The process time, for example, is preferablyadjusted such that the wettability of the substrate becomes a propervalue by previously measuring a contact angle of water under the sameconditions as the silylation processes.

The above-described resist film 6 is then formed on thesilicon-containing inorganic film 5 by application after the silylationprocess, whereby the inventive photomask blank 1 can be obtained (FIG. 2at (G)).

The applying method is not particularly limited and may be performed,for example, in the same manner as a conventional method. The thicknessof the resist film may be appropriately determined to obtain a goodpattern form.

EXAMPLE

The present invention will be specifically described below throughexamples and comparative example, but the present invention is notlimited these examples.

Example 1

The inventive photomask blank was manufactured by the inventivemanufacturing method.

A phase shift film of MoSiON with a thickness of 75 nm was formed on 152mm squares of a quartz substrate having a thickness of about 6 mm bysputtering. A gas of oxygen, nitrogen, and argon was used as asputtering gas; MoSi₂ and Si were used as two types of targets. Thesubstrate was rotated at 30 rpm to form the film.

The composition of the phase shift film was Mo:Si:O:N=1:4:1:4 (atomicratio), which was investigated by an electron spectroscopy for chemicalanalysis (ESCA) method (also referred to as an XPS method) with K-Alpha(manufactured by Thermo Fisher Scientific K.K.).

On the phase shift film, a CrN layer (30 nm) and a CrON layer (20 nm) aslight-shielding films were formed in order from a substrate side upwardby sputtering. A gas of argon and nitrogen was used as a sputtering gasfor the CrN layer; a gas of oxygen, nitrogen, and argon was used as asputtering gas for the CrON layer; a chrome metal was used as a target.The substrate was rotated at 30 rpm to form the film.

The compositions of the light-shielding films were Cr:N=9:1 (atomicratio) for the CrN layer and Cr:O:N=4:5:1 (atomic ratio) for the CrONlayer, which were investigated by the ESCA.

On the top of the light-shielding films, an SiO film with a thickness of5 nm as an etching mask film (a hard mask) containing silicon was formedby sputtering. A gas of oxygen and argon was used as a sputtering gas;Si was used as a target. The substrate was rotated at 30 rpm to form thefilm.

A heat treatment was then performed on the resultant at 500° C. under anoxygen-containing atmosphere.

The composition of the etching mask film was investigated by the ESCA;the oxygen concentration of the surface was 61.5 atomic percent.

The surface of the etching mask film was also investigated by the ESCA.FIG. 3 shows detected intensities with respect to the Si—O bond energyand with respect to the Si—Si bond energy.

From the result, it is seen that the detected intensity (the areaintensity) with respect to the Si—O bond energy is larger than thedetected intensity with respect to the Si—Si bond energy (See FIG. 3).

The resultant was subjected to the silylation process with HMDS. Afterthat, a negative type of electron beam resist (manufactured by Shin-EtsuChemical Co., Ltd.) was applied and developed with tetramethylammoniumhydroxide to obtain a resist pattern. The resultant was then rinsed withpure water.

The investigation of the resultant with a defect inspection apparatusMAGICS 2350 (manufactured by Lasertec Corporation) demonstrated a goodresult in which, as shown in FIG. 4, the number of defects was extremelysmall.

The number of detected defects having a size of 0.1 μm or more was 42.

Example 2

The inventive photomask blank in which the oxygen concentration of thesurface of the etching mask film after the heat treatment was 55.6atomic percent and the detected intensity of the Si—O bond energy waslarger than the detected intensity of the Si—Si bond energy was obtained(See FIG. 3) as in Example 1 except that the temperature of the heattreatment was changed into 300° C.

The number of defects after development was consequently 1180.

Example 3

The inventive photomask blank in which the oxygen concentration of thesurface of the etching mask film was 71.0 atomic percent and thedetected intensity of the Si—O bond energy was larger than the detectedintensity of the Si—Si bond energy was obtained as in Example 1 exceptthat the amount of oxygen in a sputtering gas was adjusted when SiO wasformed by sputtering and the heat treatment was not performed after thesputtering.

The number of defects after development was consequently 30.

Comparative Example

A photomask blank in which the oxygen concentration of the surface ofthe etching mask film was 52.6 atomic percent and the detected intensityof the Si—O bond energy was smaller than the detected intensity of theSi—Si bond energy was manufactured as in Example 1 except that the heattreatment was not performed.

The investigation of defects after development revealed that, as shownin FIG. 5, many resist residues remained. The number of detected defectshaving a size of 0.1 μm or more was 4704, which was very large.

Note that at this time, the detected intensity of the Si—O bond energywas smaller than the detected intensity of the Si—Si bond energy (SeeFIG. 3).

As seen particularly from comparison between Example 2 and ComparativeExample, Example 2 in which the oxygen concentration of the etching maskfilm surface was 55 atomic percent or more (or the detected intensity ofthe Si—O bond energy>the detected intensity of the Si—Si bond energy)greatly reduced the number of defects to a quarter or less of the numberof defects in Comparative Example in which the oxygen concentration wasless than 55 atomic percent (or the detected intensity of the Si—O bondenergy<the detected intensity of the Si—Si bond energy).

In addition, as seen from Example 1 (an oxygen concentration of 61.5atomic percent, 42 defects) and Example 3 (an oxygen concentration of71.0 atomic percent, 30 defects), it is understood that in order toinhibit the number of defects, it is sufficient to adjust the oxygenconcentration up to about 75%.

It is to be noted that the present invention is not limited to theforegoing embodiment. The embodiment is just an exemplification, and anyexamples that have substantially the same feature and demonstrate thesame functions and effects as those in the technical concept describedin claims of the present invention are included in the technical scopeof the present invention.

What is claimed is:
 1. A method for manufacturing a photomask blankhaving at least a silicon-containing inorganic film over a transparentsubstrate and a resist film on the silicon-containing inorganic film,comprising: forming the silicon-containing inorganic film such that asurface that will contact the resist film has an oxygen concentrationnot less than 55 atomic percent and not more than 75 atomic percent;performing a silylation process after forming the silicon-containinginorganic film; and then forming the resist film by application.
 2. Amethod for manufacturing a photomask blank having at least asilicon-containing inorganic film over a transparent substrate and aresist film on the silicon-containing inorganic film, comprising:forming the silicon-containing inorganic film such that when a surfacethat will contact the resist film is subjected to X-ray photoelectronspectroscopy, a detected intensity with respect to an Si—O bond energyis larger than a detected intensity with respect to an Si—Si bondenergy; performing a silylation process after forming thesilicon-containing inorganic film; and then forming the resist film byapplication.
 3. The method for manufacturing a photomask blank accordingto claim 2, wherein the silicon-containing inorganic film is formed suchthat the surface that will contact the resist film has an oxygenconcentration not less than 55 atomic percent and not more than 75atomic percent.
 4. The method for manufacturing a photomask blankaccording to claim 1, wherein hexamethyldisilazane is used for thesilylation process.
 5. The method for manufacturing a photomask blankaccording to claim 2, wherein hexamethyldisilazane is used for thesilylation process.
 6. The method for manufacturing a photomask blankaccording to claim 3, wherein hexamethyldisilazane is used for thesilylation process.
 7. The method for manufacturing a photomask blankaccording to claim 1, wherein the silicon-containing inorganic filmfurther contains at least one of oxygen and nitrogen.
 8. The method formanufacturing a photomask blank according to claim 2, wherein thesilicon-containing inorganic film further contains at least one ofoxygen and nitrogen.
 9. The method for manufacturing a photomask blankaccording to claim 6, wherein the silicon-containing inorganic filmfurther contains at least one of oxygen and nitrogen.
 10. The method formanufacturing a photomask blank according to claim 7, wherein thesilicon-containing inorganic film is an SiO film or an SiON film. 11.The method for manufacturing a photomask blank according to claim 8,wherein the silicon-containing inorganic film is an SiO film or an SiONfilm.
 12. The method for manufacturing a photomask blank according toclaim 9, wherein the silicon-containing inorganic film is an SiO film oran SiON film.
 13. The method for manufacturing a photomask blankaccording to claim 1, wherein the silicon-containing inorganic film isformed in such a manner that an inorganic film containing silicon isdeposited over the transparent substrate and then subjected to a heattreatment, an ozonation treatment, or a plasma treatment.
 14. The methodfor manufacturing a photomask blank according to claim 2, wherein thesilicon-containing inorganic film is formed in such a manner that aninorganic film containing silicon is deposited over the transparentsubstrate and then subjected to a heat treatment, an ozonationtreatment, or a plasma treatment.
 15. The method for manufacturing aphotomask blank according to claim 12, wherein the silicon-containinginorganic film is formed in such a manner that an inorganic filmcontaining silicon is deposited over the transparent substrate and thensubjected to a heat treatment, an ozonation treatment, or a plasmatreatment.
 16. The method for manufacturing a photomask blank accordingto claim 1, wherein the silicon-containing inorganic film is formed overthe transparent substrate through deposition by sputtering.
 17. Themethod for manufacturing a photomask blank according to claim 2, whereinthe silicon-containing inorganic film is formed over the transparentsubstrate through deposition by sputtering.
 18. The method formanufacturing a photomask blank according to claim 15, wherein thesilicon-containing inorganic film is formed over the transparentsubstrate through deposition by sputtering.
 19. A photomask blankcomprising at least a silicon-containing inorganic film over atransparent substrate, the silicon-containing inorganic film beingsubjected to a silylation process, and a resist film on thesilicon-containing inorganic film, wherein the silicon-containinginorganic film is configured such that a surface that contacts theresist film has an oxygen concentration not less than 55 atomic percentand not more than 75 atomic percent.
 20. A photomask blank comprising atleast a silicon-containing inorganic film over a transparent substrate,the silicon-containing inorganic film being subjected to a silylationprocess, and a resist film on the silicon-containing inorganic film,wherein the silicon-containing inorganic film is configured such thatwhen a surface that contacts the resist film is subjected to X-rayphotoelectron spectroscopy, a detected intensity with respect to an Si—Obond energy is larger than a detected intensity with respect to an Si—Sibond energy.
 21. The photomask blank according to claim 20, wherein thesilicon-containing inorganic film is configured such that the surfacethat contacts the resist film has an oxygen concentration not less than55 atomic percent and not more than 75 atomic percent.
 22. The photomaskblank according to claim 19, wherein hexamethyldisilazane is used forthe silylation process.
 23. The photomask blank according to claim 20,wherein hexamethyldisilazane is used for the silylation process.
 24. Thephotomask blank according to claim 21, wherein hexamethyldisilazane isused for the silylation process.
 25. The photomask blank according toclaim 19, wherein the silicon-containing inorganic film further containsat least one of oxygen and nitrogen.
 26. The photomask blank accordingto claim 20, wherein the silicon-containing inorganic film furthercontains at least one of oxygen and nitrogen.
 27. The photomask blankaccording to claim 24, wherein the silicon-containing inorganic filmfurther contains at least one of oxygen and nitrogen.
 28. The photomaskblank according to claim 25, wherein the silicon-containing inorganicfilm is an SiO film or an SiON film.
 29. The photomask blank accordingto claim 26, wherein the silicon-containing inorganic film is an SiOfilm or an SiON film.
 30. The photomask blank according to claim 27,wherein the silicon-containing inorganic film is an SiO film or an SiONfilm.